Electric resistance device.



PATENTED AUG. 13, 1907.

H. W. LEONARD. ELECTRIC RESISTANCE DEVICE.

APPLICATION FILED MAB.. 21. 1905.

Figi

stats, electric heaters, etc., and the essential object of IIARRY WARD LEONARD, OF BRONXVILLE, NEW YORK.

ELECTRIC RESISTANCE DEVICE.

Specication of Letters Patent.

Patented Aug. 13, 1907.

Application filed March 2l| 1905. Serial No. 251,231.

To all u'hom 'il Imay concern:

Be it known that I, HARRY WARD LEONARD, a citizen of the United States, residing at Bronxville` in the county. of Westchester and State of New York, have invented certain new and useful Improvements in Electric Resistance Devices, of which the following is a full, clear, and exact specification.

My invention relates to resistance devices and particularly to the method and means for supporting, protecting, insulating, and mechanically, electrically and chemically improving resistance devices, such as rheomy invention is to produce improvement as above stated.

One of the applications of my invention is in the manufacture of resistance units relative to which I will now describe my invention.

In making resistance units I prefer to employ a tubular support made of iictile material such as porcelain. The coeilicient of heat dilatation of such material is quite low relative to that of metals such as I prefer to employ for the'resistive conductor. For many well known reasons I prefer to use a metallic conductor embedded in a coating of adhesive material on the surface of the support. Heretofore when the resistive conductor, the support and the adhesive attaching coating are heated to a high degree in the process of manufacture the difference between the dilatation of the resistive conductor, the support, and the adhesive attaching coating, tend to impair the perfection of the said coating. One way of practically overcoming this diicnlty for many forms of apparatus is described in my Patent No. 691949, granted Jan. 28, 1902. In that patent I describe a low fusing vitreous coating which fuses and forms the adhesive attaching coating at a temperature so low that the difference in the dilatations mentioned are not enough to interfere with the commercial production of the desired article. But in many instances resistances are.desired which must withstand a development of heat such that the low fusing vitreous coating of the said patent would melt and flow, thereby exposing the resistive conductor, and displacing it, and in some instances causing the low fusing vitreous material tocollect into a thick layer on the lower side and even to cause molten drops to fall oll' in some cases.

It is desirable to employ a material for the adhesive,`r

attaching the resistive conductor to a support of different material from the coating, I prefer to use for this coating a material whose coelicient of expansion by heat is between that of the support and that of the resistive conductor.

l also prefer to use the resistive conductor in a form such as the reflexed form so that the strain in the coating will be reduced. When the conductor becomes so large as to produce detrimental strains in the coating, I prefer to sub-divide the conductor into several smaller conductors and in most cases prefer to braid together the plurality of smaller conductors, or in some equivalent way obtain the total cross section desired While avoiding the objections incidental to having a single practically straight conductor of round cross section embedded in the coating. Sometimes l use aflat metallic tape having such perfor-ations or equivalent openings as te enable the coating to iill in such openings and thereby more firmly attach the resistive conductor.

I prefer to apply the material of the coating to the support and resistive conductor while cold and then form the coating by heating in a muflle furnace or other suitable source of heat external to the resistance. In some cases however, I form the coating by developing all or a part of the heat needed by passing an electric current through the resistive conductor so as to dgavelop in the conductor itself the heat desired. The material of the coating I sometimes apply as a slip; sometimes `I apply it as a dry powder, sometimes as a paste, but in all cases I prefer to have such solid material as is employed, in a finely divided state, such as results, for example, from grinding. In some instances the coating or the protective composition need not be highly heated during the process of manufacture, a mere drying or baking being all that is needed sometimes. In many instances I prefer to glaze the coating so as to make the article more waterproof, better as regards insulation, heat and light reflecting, and securing the many well known advantages of a thin glaze on the surface of su/ch a coating. I generally apply two or more coats of the adhesive attaching coating and sometimes form the coating by repeated local applications of the material, but I may in some cases have but a single coating, or layer.

I prefer to always have in the protective composition which is in contact with -the resistive conductor a certain material whose coefficient of expansion is higher than that of the resistive conductor and another that is lower, so that by using a suitable proportion of the material of high and low coefficient of expansion, I can obtain the desired coeflicient for the protective composition. I prefer to form the protective composition so that as a whole it will not flow at a temperature below 1500 F., and is preferably formed of material which is infusible at the heat of manufacture and has combined with this only a sufficient amount of vitreous material to act as a binder. That is, the amount of fusible materi-al is so low that the composition as a whole will not be fused sufficiently to flow or assume a glazed appearance.

The following ingredients may be employed to form the composition: ground flint, ground vitreous material and fluorspar. I employ flnorspar because of its high coefficient of expansion. .Cryolite may be in some instances substituted for the fluor-spar or any similar material which is an equivalent for the purpose of increasing the coeflicient of expansion of the coating, or such materials may be combined, for example, I may use both luorspar and cryolite. It will be noted that both fluorspar and cryolite contain luorin in combination. I prefer to have a certain' amount of boron in the vitreous material. The composition described is tough, coherent, infusible as defined herein, insulating, adhcsively attaching to a support, and is protective mechanically and chemically. Moreover, its coefficient Iof expansion is well suited for use with a resistive conductor having a high coefficient of expansion, and I prefer to use such a conductor on account of the low temperature coefficient which may be secured. While the binding portion of the coating or composition is in many instances not entirely insoluble, yet it is difficultly soluble by comparison with borax, soda, saltpeter and other similar soluble-salts which are often employed principally as fluxes, in the manufacture of vitreous enamels. Therefore when I use the term insoluble inthe claims, I mean substantially insoluble and use the terin to ex, clude what are generally known as soluble salts, rather than to indicate complete insolubility.

In the accompanying drawings, Figure l is a side view of one form of myyinvention; Fig. 2 is a sectional view of one end of the construction shown in Fig. .l enlarged; Fig. 3 is an enlarged sectional view showing an additional outer coating; Fig. 4 is a plan View of a modification; Fig. 5 is a sectional view on the line 5-5 of Fig. 4; Fig` G is a sectional view showing a modification; Fig. 7 is a side view of amodification.

One suitable composition for forming the protective composition or coating contains essentially:three parts of fluorspar ground to about sixty mesh and four parts of a vitreous material made by fusing together two parts of red lead, two parts of borax and one part of flint, the said vitreous'material being ground to a fine powder. The fluorspar of said composition has a coefficient of expansion higher ythan that of cast-ironand higher than the coefficient of expansion of a resistive conductor made from an alloy of substantially sixty parts of copper and forty parts of nickel. The vitreous material of said comppsition has a coefficient of expansion less than that of cast-iron or of the said copper-nickel alloy. The composition as a whole has a coefficient of expansion between that of a cast-iron support and the said resistive alloy. When the ground uorspar is examined under a microscope, the characteristic crystalline form and refiecti'ng surface of the fluorspar crystal is readily observable and can be easily identified when again seen under the microscope. Such a microscopic examination of the protective composition after it is formed by heat, clearly discloses the fact that a large part and perhaps all of the fluorspar remains in its crystalline state and is not so fused as to eliminate the characteristic reflecting, crystallinef/snrface above referred to; that is, the fluorspar in its native state is practically embedded in a matrix of material, which latter material has been sufficiently fused to cause it to formwith the fluor-spar, a coherent composition adapted to adhere to a' suitable support when properly applied and heated in the manner well known to those skilled in the art.

Referring to Figs. l and 2, the support is indieat ed at l and is shown as tubular. This support is preferably of some mineral insulating material such as porcelain, glass, terracotta, steatite, lava, various stones, asbestos, mica, or other similar material natural or artificial or both mixed. There are many instances in which the support will be metallic and in that case the coating will be of sufficient thickness to insure goed insulation of the conductor from the metallic support. The resistive conductor is indicated at 2 and is shown in the form of a fiat braid of wire having an open mesh and as more particularly described in my Patent No. 787,047, granted April ll, 1905. The conductor is embedded in the infusible coating 3 which I have above described and is wound around the support. The conductor is united at the ends to braided terminal leads 4 which are seated in grooves 5 formed inthe support and which terminal leads, where they encircle the support, are likewise embedded in the coating.

In Fig. 3 which shows a sectional view of a portion of ai resistance unit, there is shown in addition to the in.- fusible coating in which the conductor is embedded, a coating G of vitreous material such as glass enamel, and I thereby secure the advantages of a glazed surface as above referred to.

In Figs. 4 and 5 I have shown a support in the form of a plate 7 which may be of iron, or other suitable material. The conductor 8 is shown as refiexed and connected to the terminal contacts 9, the conductor and portions of the terminal contactsbeing embedded in the infusible coating 3. In some cases the conductor may be only partially embedded, for example, as shown in Fig. 6, in which the conductor l0 is in the form of a reflexed ribbon, having one edge embedded-in the insulating material.' In-some cases this resistive conductor will not itself be embedded in the coating, but will 'have its terminals or supports embedded or partially embedded in the coating. In some cases the coating itself may form the only support in the finished article. That is, the coating or protective composition may be formed about the conductor so as to form a support in itself, or a temporary support may be employed during manufacture which will not be present in the finished article.

In Fig. 7 I have indicated a spirally formed conductor ll for which there is no other support than the coating or protective composition 3, being somewhat similar t0 the construction shown in Figs. l and 2 except there is no supporting tube. The unit, as shown, is provided with rigid supporting terminals l2 which are fixed to the base plate 13. i

It will be understood that various other forms of construction may be developed which will he within the scope of my invention.

Whenever I use the word powdered in the claims I mean to describe a material in a finely divided state whether it be dry, or mixed -with a fluid so as to be paste-lille or (ement-like, or whether it be suspended v in a liquid so as to be paint-like. Whenever I use the word infusible in the claims I mean to describe a material which when subjected t0 the heat under consideration does not become soft or viscous as a whole, or form a glazed appearance although certain ingredients therein, when considered separately, may become more or less soft or viscous. The material is such that it retains a dull, pottery like surface afterl being subjected to a visible-red heat. Whenever I use the words vitreous material in the claims I mean to describe a material which has been melted by heat to form a material resembling glass for the purposes hereof. By the term embedding as used in the claims, I mean either wholly or partiallysurrounding the conductor and with or without an additional support. Whenever I use the word glazed I mean to describe a polished insulating surface impervious to moisture.

Having thus described my invention7 I declare that what I claim as new and desire to secure by Letters Patent, is,-

1. The combination of a resistive conductor, and an infusible composition embedding the conductor, said composition containing uorin and containing only insoluble materials as essential ingredients when applied to the conductor.

2. The combination of a resistiveconductor, and an infusible composition embedding the conductor, said composition containing fluorspar and containing only insoluble materials as essential ingredients when applied to the conductor.

3. The combination of a resistiveconductor, and an infusibie composition embedding the conductor, said composition containing i'luorin and boron and containing only -insoluble materials as essential ingredients when applied to the conductor.

4. lhecombination of a resistive conductor, and an insulating heat resisting composition about said conductor, said composition containing i'luorspar in its native state but finely divided and disseminated through the composition and containing only insoluble materials as essential ingredients when applied to the conductor.

5. The combination of a resistive conductor, and a layer of insulating material adhesively attached thereto, said insulating material containing finely divided iluorspar and a bindingmaterial, whereby an adhesive layer is produced.

(i. The combination of a Support, a resistive conductor, and an insulating,r coating embedding said conductor, said coating being cohesive and adhesive to the support, infusible, and containing an ingredient whose coefficient of ex pansion is higher than that of said conductor.

7. The combination of a resistive conductor, and a coatlng embedding and protecting said'conductor, said coating being coherent and insulating and formed of material part of which is infusible at the heat of manufacture and part of which is fusible, the proportion of fusible material being so low that the coating as a whole is infusible, and

p said coating containing an ingredient whose coefficient of expansion is higher than that of said conductor.

8. The combination of a resistive conductor, and a solid insulating material embedding said conductor, said materini being composed of one ingredient havinga coefiicient oi' expansion higher than that of the conductor and another which has a Vcoefficient of expansion less than that of the conductor, one of said ingredients being infusible during the process of manufacture and another being softened by heat during manufacture suiliciently to hind the ingredients into a coherent mass.

9. The combination of a resistive conductor, and a solid insulating material embedding said conductor, said material composed of different ingredients one of which is fu sible and another oi' which is infusibie and having a coefficient of expansion higher than that of the conductor.

10. 'ihe combination of a resistive conductor, a support, und un insulating material embedding said conductor und adheslvely engaging the support, said material containing :is .one ingredient an infusible substance having `a coeflicieut of expansion higher than that f the conductor, and

containing another ingredientA in the form of a vitreous material which serves to bind the parts together in the form of a solid coherent mass.

11. The combination of a resistive conductor, said conductor being in the form of a braid, and an insulating material embedding'said conductor, one ingredient of said material having a coeiiicient of expansion higher than that ot the conductor.

I 12. The combination ofa resistive conductor, an insulating material embedding said conductor, said material being infusible, and an outer coating of vitreous material.

13. The combination of a resistive conductor, said conductor having a low temperature cociiicient and a high coeiiicient of expansion, and an insulating material embedding,r said conductor, said material being infusible and containing an ingredient whose coefficient of expansion is higher than that of the conductor.

14. The combination of a resistive conductor, and an insulating material embedding said conductor, said material beingformed of different ingredients, one of said ingredients having a coefficient of expansion higher than that of said conductor and the said coefficient of expansion being substantially unaffected by the heat of manufacture.

15. The combination of a support, a resistive conductor having a coeicient of expansion higher than that of the support, and a coating which attaches the conductor to the support, the coeftcient of expansion of the coating being higher than that of the support and less than that of the resistive conductor. V

16. The combination of a resistive conductor, and an inA lsulating, protective, supporting,'heat conducting, infusible material embedding said conductor, said coating being applied to the conductor in the form of a powder and formed by heat into a coating which is infusibie and adhesive, said coating containing at least one ingredient whose coeicient of expansion is higher than that of said conductor.

17. The combination of a resistive conductor, and a pro-.

tective insulating material embedding said conductor, said material being applied as a powder and formed by heat into a tough coherent layer of insulating material and which is subjected to a heat sutiicient to cause the powdered material to cohere without causing the coating as a whole to fuse enough to iiow or to obtain a glazed surface, said coating containing at least one ingredient whose coeiiicient of expansion is higher than that of said conductor.

18. The combination of a resistive conductor, and an insulating, infusible composition adherent thereto, said composition containing tluorspar or its equivalent.

19. The combination of a resistive conductor, and an insulating, infusibie omposition adherent thereto, said composition containing in its native state a mineral having n coeiiicientA of expansion higher than that of the conductor and a binding material.

20. The combination of a support of insulating material, a resistive conductor, said conductor having a coeticient of expansion higher than that of said support, and a layer of insulating material applied in a iinely divided state and forming a. solid layer of material in which said conductor is embedded,the coetiicient of expansion of said layer of material being between that of said conductor and that of said support.

21. The combination of a cylindrical support of insulating material, a resistive conductor, and a layer of insulating material applied in a iinely divided state and forming a solid layer of material in which conductor is embedded, said layer of material havingr a coeiiicient of expansion between that of said support and that of said conductor.

22 The combination of a cylindrical support of insulating material, a resistive conductor, and a layer of insulating material upon `said support and in which said conductor is embedded, said layer of insulating material containing an ingredient having a coeiiicient of expansion higher than that of said support and higher than that of said conductor.

In teltimony whereof I nilx my signature, in presence of two witnesses.

ll` WARD LEONARD. Witnesses:

L. K. Sacmi, Gao. A. HOFFMAN. 

